The invention relates generally to portable remotely powered communication devices and to systems for powering up and receiving information from such devices, and more particularly, to such devices and systems that employ electrostatic coupling.
Remotely powered electronic devices and related systems for powering up and receiving stored information from such devices are well known. For example, U.S. Pat. No. 4,818,855 issued to Mongeon et al., entitled, Identification System, discloses a remotely powered identification device which derives power from a remote source via one of an electric field or a magnetic field and which transmits stored information back to the source via the other of the electric field or magnetic field. Similarly, U.S. Pat. No. 5,099,227 issued to Geiszler et al., entitled, Proximity Detecting Apparatus, discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source and which uses both electromagnetic and electrostatic coupling to transmit stored data back to the source.
In the earlier systems described above, an electromagnetic mechanism is used to remotely couple the remote device with either one or both of an exciter system and a receiver system. The exciter generates an excitation signal used to power up the device. The receiver receives the signal produced by the remote device. One reason for the use of electromagnetic coupling in prior devices is that it was believed to be more efficient to remotely couple power from an exciter to a device via an electromagnetic field rather than via an electrostatic field. Moreover, it was believed that in order to employ an electrostatic mechanism to couple energy from an exciter to a remote device using a single-plate antenna, relatively high voltage signals were required. However, the ability to emit higher voltage signals for power up often is limited by FCC regulations.
Earlier electromagnetic coupling mechanisms included an oscillator as part of the exciter circuitry and coil antennas mounted on both the exciter circuitry and a tag or other article that embodied the device and contained its electronic circuit. For example, in one earlier system excitation circuitry is connected to a coil antenna which radiates excitation signals that are picked up by a coil antenna mounted on a tag that contains the electronic circuit. The excitation signals energize the electronic circuit which automatically produces an information carrying signal that is transmitted to the receiver using electromagnetic or electrostatic coupling.
An ongoing objective in the development of remote communication devices and associated exciters/receivers of the general type described above has been to minimize cost and size and to improve efficiency of operation. A problem with the use of electromagnetic coupling between a remote device and either an exciter or a reader has been the additional complexity involved in the manufacture of remote devices that employ a coil antenna. For example, the spiral layout of a typical coil antenna can be more difficult to produce than the simpler layout of an electrostatic antenna which often can be in the form of a straight wire or planar and plate-like. Another problem, explained above, has been the inability to efficiently couple power electrostatically using acceptable voltage levels. As a consequence, electromagnetic coupling generally has been favored over electrostatic coupling.
Thus, there has been a need for a low cost remotely powered communication device that employs electrostatic coupling both for remote power up and for the transmission of information carrying signals. There also has been a need for an improved method and apparatus for coupling electrostatic power up signals to such a device. The present invention meets these needs.